Counterbalancing mechanisms have been employed for many years. Common examples of use for such systems are garage doors in homes, commercial and industrial buildings, or sliding truck doors. In some applications, they may be used with windows or other kinds of panels. Counterbalancing mechanisms provide a mechanical assistance for facilitating the opening and closing of these movable items. They allow a person to manipulate them easily and to use a smaller motor when powered assistance is provided.
The counterbalancing mechanisms that use torsion springs enjoy an increasing popularity in the industry. They generally comprise a pair of spaced-apart cable drums connected to flexible cables which, in turn, are connected to corresponding lower parts of the door, for instance. The cable drums are mounted around a shaft that is transversely located above the door opening. The torsion springs, coaxially located on the shaft, are each secured at one end to a corresponding cable drum. The other end of each torsion spring is secured to a fixed location, such as a bracket, itself rigidly attached to a wall or the ceiling. The torsion springs are biased to rotate in a direction which winds the cables onto the cable drums. The spring torque is adjusted to properly balance the weight of the door so that minimum opening and closing effort is required, either manually or motor controlled.
In use, each end of a torsion spring is connected to an adjacent component by means of a plug. The plug usually comprises a body having an outer surface with a plurality of grooves forming threads for receiving the corresponding end coils. The plugs are generally provided with superposed right-hand and left-hand threads, as disclosed in U.S. Pat. No. 3,779,537 of 1973 to Kalister. Each plug is connected to an adjacent component, such as a cable drum, a gear, a wall bracket or even the shaft, by means of fasteners. Examples of fasteners are screws, bolts or the like. One drawback of this situation is that the installation with fasteners is time consuming and tedious. Also, the use of fasteners is very difficult when securing a loaded spring to an adjacent component.
Alternatively, the plug may be molded or cast with the component to create a single integrated part. This creates the need of having inventories of many parts to accommodate all possible situations.